Servo arm strength
 

I have been looking at every single post here, trying to learn as much as I can... Will be getting an AD Phoenix as soon as they are available... I repeatedly see pics of people using stock servo arms on their control surfaces.... On my big planes, always used metal arms in fear that the big surfaces would rip the splines off a nylon servo wheel. I know the surfaces are smaller on jets, but I figured the speed 150mph + would make it about even the forces the servos are seeing compared toa big plane... I have also seen regular clevis type connectors....

Whats the deal? Is it overkill to use metal servo arms? I would think the HD ball link type connections would be ideal with turnbuckles....


thanks, Mike

RE: Servo arm strength
 

The times I use metal arms is not due to concern about splines stripping but due to concrens about flexing. A heavy duty 4-40 clevis is very strong as long as the plane of rotation for both the control surface horn and the servo arm are in the same plane. If the servo is installed 90 degrees to the horns rotation then the axial displacement of the rod can be too big with 3D type control surface movements and it'll cause the clevis to want to open up. In that case you would want to go to a heavy duty ball link and that is the reason for switching to a metal arm since the ball link will cause a plastic arm to twist and even snap off with heavy sharp loads.

RE: Servo arm strength
 

Metal horns are not an overkill on jets. I lost my Eurosport because of a stripped nylon horn

Zane

RE: Servo arm strength
 

Metal servo arms are used when you need a long arm application, like a 3D airplane, to avoid flexing as stated above. Jet models are different, you should always strive for a short servo arm and in this case the standard servo wheels will do fine, and anyway, if you don´t get peace of mind
by using plastic horns on the airplane, you shouldn´t have it too using servos with plastic cases! ;)
Heavy duty ball links are also used without problems in any particular aplication that needs some
angular movement on the linkage, otherwise, du-bro 4/40 metal clevises are the norm.

Best regards, Enrique

RE: Servo arm strength
 

At last some sense...
There is huge overkill on the types of hardware/servos used in jet models. I used to fly a Trim Spectre (recorded 167MPh in a dive) with a single Futaba 3001 servo and a plastic horn on the elevator. I logged 3 years of regular flights with no problems.
Just use some common sense and make sure you get the geometry correct use a short servo arm to get the most torque. Discs are the best option for strength before using a metal arm. hope this helps also...

RE: Servo arm strength
 

Hi Guys,


I fly jets and run 1/5 scale cars. What I do is to cross some of the tips from one side to another. If you see how the servos on a steering are install in a car with turnbuckles and ball links you will not have troubles ever, the punishment that we give to those systems is the worst you can do to test a servo and the horns. So check it out and just transfer it to the jet.

Leon G. ;)

RE: Servo arm strength
 

Overkill...Perhaps, but with 10K flying around, Overkill is better than inadquate [:@]